The present invention relates to a detector and especially relates to a detector being used for a microwave band power amplifier etc.
A conventional detector will be explained with reference to FIG. 1. In FIG. 1, a reference numeral 1 denotes a main transmission line and resistances R2 and R3 are connected to the main transmission line 1. And then, a part of the microwave power that propagates on the main transmission line 1 is divided by resistances R2 and R3. The divided microwave power is converted to a voltage by a detection diode CR4, and then direct current voltage is obtained by a smoothing capacitor C5.
The elements R2, R3, CR4 and C5 constituting the detector are closely connected with each other and the detector including the elements R2, R3, CR4 and C5 has good characteristics like (1) to (3) as following since the elements R2, R3, CR4 and C5 are closely connected to the main transmission line 1.
(1) The frequency response of the detection voltage has good characteristics.
(2) The precision of the detection voltage that is decided by the partial voltage by the resistances R2 and R3 is improved.
(3) The whole circuit becomes a small size.
As described above, the detector has good characteristics. However, the characteristics of the detection diode CR4 are adversely affected by coupling to the main transmission line 1, that is, a capacity between the main transmission line 1 and detection diode CR4 becomes large since the elements R2, R3, CR4 and C5 are closely provided with the main transmission line 1.
By the way, the distance between the elements R2, R3, CR4, C5 and main transmission line 1 becomes about 2 to 3 mm since each of the elements R2, R3, CR4 and C5 is about 2 to 3 mm per side. Therefore, the characteristics of the detector are influenced by the coupling adversely affecting the characteristics thereof from main transmission line 1 in such a distance.
The conventional detector that decreases the influence of the power radiation will be explained with reference to FIG. 2.
As shown in FIG. 2, the microstrip line 7 that has the length of a 1/4 wavelength of a propagation signal is formed in parallel with a main transmission line 6. One end 7a of the microstrip line 7 is grounded via a resistance R8 and another end thereof is connected to the detection diode CR9. The detection voltage is obtained by the detection diode CR9, and then, a direct voltage is obtained by the smoothing capacitor C10.
In the case of such a detector, an output power is detected by the spatial coupling between the main transmission line 6 and microstrip line 7.
In the detector, it can make the another end 7b of microstrip line 7 long and make the main transmission line 6 separate from the detection diode CR9. Therefore, the influence of the detection diode CR9 in characteristics can be prevented.
However, there is a problem that the main transmission line 6 requires a 1/4 wavelength in parallel with the microstrip line 7 to obtain a degree of spatial coupling between the main transmission line 6 and microstrip line 7 in such the detector. Furthermore, there is a problem that the dispersion occurs in the detection voltage because of variations in the coupling characteristic between the main transmission line 6 and microstrip line 7.
In the conventional detector as shown in FIG. 1, the detector can be made a small size since the constitution elements are closely connected to the main transmission line 6.
However, on the other hand, there is a problem that the characteristic degrades by the coupling adversely affecting the characteristics of the detector.
In the conventional detector shown in FIG. 2, the main transmission line 6 is formed in parallel with the micro strip line. Therefore, the degradation of characteristics by the coupling adversely affecting the characteristics of the detector from the main transmission line decreases. Furthermore, there is a problems that the dispersion occurs in detection voltage by the dispersion of coupling characteristics and that the regular length becomes necessary to a main transmission line.